Polarization-independent optical switch/attenuator

Abstract

An optical device which controls the strength of an optical signal from an input fiber to an output fiber responsive to a signal on a control terminal. The device has a first GRIN lens associated with the input fiber, a first birefringent polarizer, a liquid crystal cell, a second birefringent polarizer and a second GRIN lens associated with the output fiber. The liquid crystal cell, located between the first and second polarizers and connected to a control terminal, controllably rotates the optical signal from the optical axis of the first polarizer toward the optical axis of the second polarizer responsive to the signal on said control terminal. The operation of the device is independent of the polarization of the optical signal in the input fiber. Furthermore, the device can be operated as an optical switch or an optical attenuator by suitably arranging the axes of the polarizers and liquid crystal cell.

What is claimed is: 
     
       1. An optical device for connection to an input optical fiber and an output optical fiber, said device having at least one control terminal, said device controlling the strength of an optical signal from said input fiber to said output fiber responsive to a signal on said control terminal, said device comprising a first GRIN lens arranged to collimate said optical signal from said input optical fiber;   a first birefringent polarizer having an optical axis perpendicular to a line of travel from collimated optical signal from said first GRIN lens, said first polarizer arranged to split said optical signal from said first GRIN into two polarization modes;   a second birefringent polarizer having an optical axis perpendicular to said line of travel from collimated optical signal from said first GRIN lens and offset from said optical axis of said first polarizer by a predetermined angle;   a second GRIN lens arranged to recollimate said optical signal from said second polarizer to said output fiber; and   means, disposed between said first and second polarizers and connected to said control terminal, for controllably rotating said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer responsive to said signal on said control terminal;   whereby performance of said device is independent of polarization of said optical signal in said input fiber.   
     
     
       2. The optical device of claim 1 wherein said rotating means comprises a liquid crystal cell. 
     
     
       3. The optical device of claim 2 wherein said liquid crystal cell comprises smectic liquid crystal. 
     
     
       4. The optical device of claim 3 wherein said smectic liquid crystal is ferroelectric. 
     
     
       5. The optical device of claim 2 wherein said liquid crystal cell comprises nematic liquid crystal. 
     
     
       6. The optical device of claim 1 wherein said control signal has two states, one state corresponding to a full rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer, the other state corresponding to no rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer, whereby said device operates as an optical switch. 
     
     
       7. The optical device of claim 6 wherein said predetermined angle is 90 degrees whereby said optical signal may be switched fully off and on. 
     
     
       8. The optical device of claim 1 wherein the amount of rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer corresponding to the strength of said control signal, whereby said device operates as an optical attenuator. 
     
     
       9. The optical device of claim 8 wherein said predetermined angle is 90 degrees whereby said optical signal may be attentuated completely. 
     
     
       10. The optical device of claim 2 wherein said first and second polarizers comprise lithium niobate. 
     
     
       11. An optical device for connection to an input optical fiber and an output optical fiber, said device having at least one control terminal, said device controlling the strength of an optical signal from said input fiber to said output fiber responsive to a signal on said control terminal, said device comprising a first GRIN lens arranged to collimate said optical signal from said input optical fiber;   a first birefringent lithium niobate polarizer having an optical axis perpendicular to a line of travel from collimated optical signal from said first GRIN lens, said first polarizer arranged to split said optical signal from said first GRIN into two polarization modes;   a second birefringent lithium niobate polarizer having an optical axis perpendicular to said line of travel from collimated optical signal from said first GRIN lens and offset from said optical axis of said first polarizer by a predetermined angle;   a second GRIN lens arranged to recollimate said optical signal from said second polarizer to said output fiber; and   a liquid crystal cell, disposed between said first and second polarizers and connected to said control terminal, for controllably rotating said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer responsive to said signal on said control terminal;   whereby performance of said device is independent of polarization of said optical signal in said input fiber.   
     
     
       12. The optical device of claim 11 wherein said control signal has two states, one state corresponding to a full rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer, the other state corresponding to no rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer, whereby said device operates as an optical switch. 
     
     
       13. The optical device of claim 12 wherein said predetermined angle is 90 degrees whereby said optical signal may be switched fully off and on. 
     
     
       14. The optical device of claim 12 wherein said liquid crystal cell comprises smectic liquid crystal. 
     
     
       15. The optical device of claim 14 wherein said smectic liquid crystal is ferroelectric. 
     
     
       16. The optical device of claim 12 wherein said liquid crystal cell comprises nematic liquid crystal. 
     
     
       17. The optical device of claim 11 wherein the amount of rotation of said optical signal from said optical axis of said first polarizer toward said optical axis of said second polarizer corresponding to the strength of said control signal, whereby said device operates as an optical attenuator. 
     
     
       18. The optical device of claim 17 wherein said predetermined angle is 90 degrees whereby said optical signal may be attentuated completely. 
     
     
       19. The optical device of claim 17 wherein said liquid crystal cell comprises smectic liquid crystal. 
     
     
       20. The optical device of claim 19 wherein said smectic liquid crystal is ferroelectric. 
     
     
       21. The optical device of claim 17 wherein said liquid crystal cell comprises nematic liquid crystal.